Share your experience!
hi guys, my vayo can not see additional 256 module in slot no.2
have tried in slot no.1 and working okay, will appreciate your advice.
Hi Walter449 and welcome to Club Vaio.
I wonder if your Vaio is suffering fron the well documented Vaio Memory Slot Problem which affects the GRX-Series.
http://www.aqstech.com/vaio.html
Have a look at this long thread in HardwareAnalysis: -
http://hardwareanalysis.com/content/topic/5449/
You will have to consider if a repair is viable - we did have a contact for repairs, I'm sure someone with a better memory than me will remember.

Hi Blencogo
I think Bruce Benson was the guy who repaired Sony Vaio memory sockets..
If it is the correct guy I think he lives in the Peterborough area.. 
Thanks a lot, now all clear.